Preheat the oven to 400°.
Scrub the potatoes and pierce each one a few times with a thin-bladed knife to prevent them from popping open while baking.
Place on a 9- × 12-inch foil-lined baking pan and bake about 1 hour, or until very soft.
Meanwhile, in a dry skillet over medium heat, toast the pumpkin seeds until they are lightly browned and pop around in the pan.
Remove to a bowl and reserve.
When the potatoes are done, remove from the skins and mash with the butter.
Season with salt and pepper.
Stir in the toasted pumpkin seeds.